page_title: Wolves and moose on Isle Royale
section_title: Wolf-moose dynamics interactions
hierarchical_section_title: Wolves and moose on Isle Royale / Wolf-moose dynamics interactions
caption_attribution_description: English: Moose, Superior National Forest, Minnesota, USA
context_page_description: The single predator-single prey relationship between wolves and moose on Isle Royale in Lake Superior is unique, and has been the subject of detailed study for over 50 years. Isle Royale, the principal island of Isle Royale National Park in Michigan in the United States, is an isolated island with little migration of animals into and out of the island, and as a national park, human interaction and impact on the two species is also limited. Both the wolves and the moose first became established populations on Isle Royale in the 1900s. Over the fifty years of the study, the populations of both moose and wolves have shown repeated spikes and declines and have not settled to a balanced relationship. The moose populations have ranged from 500 to 2500 while the number of wolves has ranged from almost 50 to down to two. As of 2018, wolves are being released at Isle Royale in hopes of bringing back the wolf population.
  The relationship between wolves and moose on Isle Royale has been the subject of the longest predator-prey research study, begun in 1958. The wolves have been subject to inbreeding and carry a spinal deformity.
context_section_description: As an isolated island, Isle Royale initially had neither wolves nor moose. The moose are believed to have either swum across Lake Superior from Minnesota in the early 1900s or were stocked on the island by man for the purpose of recreational hunting.  In 1949 a pair of wolves crossed an ice bridge from Ontario to the island during a harsh winter. But because only one pair of wolves migrated to the island, they have suffered from severe inbreeding. According to Rolf Peterson, a professor at Michigan Technological University and the lead wolf-moose researcher, "Moose were isolated here 100 years ago. Most of the genes are still here, but they have enough population (to compensate). There are so few wolves that they have lost genetic variability. The scientific dogma suggests that they are not going to make it."  In fact, all of the wolves' DNA on Isle Royale can be traced back to one ancestor.  Inbreeding leads to inbreeding depression and fitness problems, often accompanied by violent social rejection by other wolves.
  When the study began in 1958, many researchers believed the two species would eventually reach a population equilibrium of about 25 wolves and 1,500 moose; but there has been no sign of this, with populations fluctuating unpredictably.  The highest number of moose observed since the arrival of wolves was 2,450 in 1995. The highest number of wolves observed was 50 in 1980 followed by a population crash to 14 by 1982.  As of 2005, there were 540 moose, the lowest recorded, and a relatively high population of 30 wolves. In 2008, there were 700 moose and 23 wolves.
  The density of the two species depends strongly on the density of forage. Moose prefer birch and aspen trees, which used to grow plentifully on the island, but over a century of moose browsing have been largely replaced by the less nutritious balsam fir, which now makes up 59% of a moose's diet. Even this has declined dramatically: as of 2002, understory growth of balsam fir was at 5%, down 40% from 19th century observations.  The plant is more plentiful on the east side of the island, which draws a higher concentration of moose.  Because balsam fir does not give sufficient moisture, moose have recently been spotted eating snow, a very rare occurrence.  They have also been sighted eating lichen, which researcher Rolf Peterson has compared to eating dust.  When the moose population grows too high, the balsam fir population crashes, leading to a crash in the moose population, in a continuing population "see-saw". Moose mostly die from the consequences of malnutrition: they become emaciated and slowed down by arthritis, until they are easy prey for a wolf pack. Also, calves suffer from malnutrition when they are born during a winter with snow too deep for easy foraging.
  Moose make up nine-tenths of an Isle Royale wolf's diet (the remainder being snowshoe hare and beaver). Moose in their prime years commonly outrun wolves in a hunt, especially on soft snow: moose can cross snow two feet deep at 20 mph (32 km/h).  Even if wolves can catch up to a moose, they cannot always bring it down; researchers often find wolves with hunting bruises and scars.  To improve their chances, wolves pick out moose which are calves, old, diseased, or injured. The typical moose killed is about 12 years old and suffers from arthritis, osteoporosis, and/or periodontitis.  Eighty to ninety percent of moose are brought down by wolves rather than directly by disease, and each wolf kills an average of between 0.44 and 1.69 moose per month.
caption: Moose health and population on Isle Royale have a great effect on other animal and plant life.
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